Various types of sewing threads and the methods of making them are well known in the art. Typically, sewing threads fall into four types; (1) spun threads, (2) core threads, (3) continuous filament threads, and (4) air entangled threads. My invention relates primarily to the first type, spun threads. In general, all sewing threads are formed from a combination of individual yarns and these yarns are manufactured in differing ways and composed of differing materials. Spun threads are characterized in that the individual yarns or singles are fabricated from small pieces of staple through a drafting and twisting process commonly known as spinning. The staple fiber is typically composed of natural fibers or small pieces of synthetic filaments less than 2 inches in length, however, when aramid and/or meta-aramid fibers are used those fibers may exceed 2 inches in average length.
Conventional spun threads are commercially manufactured in a series of process steps which begins by spinning bulk staple fibers into multiple small spinning bobbins of spun yarn. The staple fiber can be synthetic, natural or a mixture of each. The spinning step, typically ring spinning, not only takes the small pieces of staple fibers and creates a continuous spun yarn or single, but also imparts a quantifiable amount of twist in the singles, which is measured in turns per inch. These multiple small bobbins of singles are then used in a single end winding process where the individual singles are joined together end to end to make larger bobbins of continuous spun yarn. The single end winding process also typically employs “yarn clearers” that remove imperfections in the singles, which are commonly referred to as “slubs” or “fly.” Then, two or more of the spun yarns are combined together in a doubling process to make a unitary composite of spun yarn, where each individual spun yarn has the same amount of twist, all in the same direction. The direction of this twist is typically referred to as the S direction. The unitary composite of two or more singles is then twisted in the opposite direction (the Z direction) to a level of twist that is typically less than 3 turns per inch when compared to the twist of the individual spun yarns or singles. At this point the sewing thread can be further processed or “finished.” Finishing can be a single step or multiple steps and can include lubricating, heat setting, coating, dying or other commonly known finishing steps to enhance thread performance.
In contrast to spun threads, both core threads (also known as “core spun threads”), continuous filaments, and air entangled threads each contain at least one continuous filament or bundle of filaments of synthetic material, typically acrylic, nylon, polyester, polyethylene, or mixtures thereof. In core threads, staple is spun over and around the continuous filaments or bundle of filaments to form a “core spun yarn.” Two or more of these core spun yarns are plied together and twisted to form the core spun sewing thread. The “core” of continuous filament(s) gives the finished sewing thread high strength and durability. In some cases, a natural staple, such as cotton, may be spun around the continuous synthetic filament(s). The air entangled sewing thread is somewhat similar to the core thread in that it contains yarns that are made of continuous synthetic filaments. An air jet is used to disrupt the bundle of continuous filaments in an overfed yarn which causes it to entangle with one or more of the other continuous filaments to produce a textured final thread product. The common element of both air entangled and core threads is the use of continuous filaments of synthetic polymer material. Spun threads on the other hand contain no continuous filaments. When threads containing continuous filaments are compared to spun threads in sewing applications that require multi-directional sewing, those threads containing the continuous filaments generally have less breakage than that of spun threads. Less breakage translates into less operator and/or machine downtime which directly translate into a cost saving for each manufactured piece. In addition, threads containing continuous filaments generally withstand or hold-up better than spun threads when the sewn into garments that are subjected to abrasive treatments, such as stone washing of fabrics like denim.
One advantage of spun threads over core or entangled sewing threads, from a manufacturing or raw material cost point of view, is that spun threads are the least expensive of the three types of threads to manufacture because the cost of staple fiber is much less expensive than that of continuous filaments. However, from a performance point of view, i.e., sewability and durability, spun threads are less desirable than threads containing continuous core filaments. The differences are more evident during heaving sewing applications and/or when the thread undergoes abrasive treatment such as occurs in the commercial stone washing of denim jeans. In these environments, spun thread has a tendency to fray or break and generally does not perform as well as threads where the individual yarns or singles contain a continuous filament core. Accordingly, there exists a need to develop an improved spun thread that contains the less expensive staple but exhibits performance greater than conventional spun thread and more preferably approaches or equals that of core thread. I have now determined that by imparting a high twist to the individual spun yarns, which is contrary to established manufacturing doctrine, that I can produce a ply twisted composite thread having two or more yarns, where at least one single composed of 100% staple fiber. Such an improved spun thread exhibits performance almost equal to that of a conventional core type sewing thread.
Accordingly, it is an object of my invention to provide a sewing thread comprising staple fiber that has superior performance when compared to conventional spun thread made from 100% spun staple.
It is a further object of my invention to provide a sewing thread made from staple fiber that exhibits performance and durability approaching or equaling that of conventional core threads.
Yet a further object of my invention involves a method of manufacture that will produce the improved spun sewing thread of my invention. These and other objects and embodiments will become evident from the following description of my invention and the appended claims that define my inventions.